Utilizing an ionic liquid for synthesizing a soft matter polymer ``gel'' electrolyte for high rate capability lithium-ion batteries

A cross-linked polymer ``gel'' electrolyte obtained from free radical polymerization of a vinyl monomer (acrylonitrile; AN) in a room temperature ionic liquid electrolyte (N,N-methyl butyl pyrrolidinium-bis (trifluoromethanesulphonyl)imide-lithium bis(trifluoromethanesulphonyl) imide;LiTFSI-[Py(1,4)-TFSI]) for application in high rate capability rechargeable lithium-ion batteries is discussed here. This is a novel alternative compared to the often employed approach of using a molecular liquid as the medium for performing the polymerization reaction. The polymer ``gel'' electrolytes (AN:Py(1,4)-TFSI = 0.16-0.18, w/w) showed remarkable compliable mechanical strength and higher thermal stability compared to LiTFSI-[Py(1,4)-TFSI]. Despite two orders increase in magnitude of viscosity of polymer ``gels'', the room temperature ionic conductivity of the ``gels'' (1.1 x 10(-3)-1.7 x 10(-3) Omega(-1) cm(-1)) were nearly identical to that of the ionic liquid (1.8 x 10(-3) Omega(-1) cm(-1)). The present ``gel'' electrolytes did not exhibit any ageing effects on ionic conductivity similar to the conventional polymer gel electrolytes (e.g. high molecular weight polymer + salt + high dielectric constant molecular solvent). The disorder (ionic liquid) to a relative order (cross-linked polymer electrolyte) transformation does not at all influence the concentration of conducting species. The polymer framework is still able to provide efficient pathways for fast ion transport. Unlike the ionic liquid which is impossible to assemble without a conventional separator in a cell, the polymer ``gel'' electrolyte could be conveniently assembled without a separator in a Li vertical bar lithium iron phosphate (LiFePO(4)) cell. Compared to the ionic liquid, the ``gel'' electrolyte showed exceptional cyclability and rate capability (current density: 35-760 mA g(-1) with LiFePO(4) electronically wired with carbon (amorphous or multiwalled nanotube [MWCNT]).

Study of ion solvation and ion association in polymer gel electrolyte with polyethylene oxide-co-polypropylene oxide as a plasticizer

Using a molal conductance method, ion solvation and ion association in polytriethylene glycol dimethacrylate (PTREGD)-LiClO4 gel electrolytes with amorphous ethylene oxide-co-propylene oxide (EO-co-PO, <(M)over bar (n)>, = 1750) as the plasticizer were investigated. It was found that the fraction of solute existing as single ions (alpha(i)) and ion pairs (alpha(p)) decreases, while that of triple ions (alpha(t)) increases linearly with increasing salt concentration. The dependence of these fractions on molecular weight of plasticizer was also examined. It was shown that alpha(i) and alpha(t) increase and alpha(p) decreases with increasing molecular weight. The result of temperature dependence of these fractions was very interesting: when the temperature is lower than 55 degrees C, alpha(i) increases while alpha(p) and alpha(t) decrease with increasing temperature; however, when the temperature is higher than 55 degrees C, the reverse is true.

The conductivity behavior of a polymer gel electrolyte

A new kind of polymer gel electrolyte which is composed of polytriethylene glycol dimethacrylate(PTREGD), propylene carbonate(PC) and LiPF6 has been prepared by thermal polymerization. The conductivity was measured as a function of temperature, and it was found that the Arrhenius equation was held very well through out the salt concentration studied. Maximum room temperature conductivity of 4.95 x 10(-4) S/cm, as well as a minimum activation energy value of 18.90 kJ/mol were obtained at the same salt concentration of 0.22 mol/L.

Pt-based anode catalysts for direct ethanol fuel cells

In the present work, several carbon supported PtSn and PtSnRu catalysts were prepared with different atomic ratios and tested in direct ethanol fuel cells (DEFC) operated at lower temperature (T=90 degreesC). XRD and TEM results indicate that all of these catalysts consist of uniform nano-sized particles of narrow distribution and the average particle sizes are always less than 3.0 nm. As the content of Sn increases, the Pt lattice parameter becomes longer. Single direct ethanol fuel cell tests were used to evaluate the performance of carbon supported PtSn catalysts for ethanol electro-oxidation. It was found that the addition of Sn can enhance the activity towards ethanol electro-oxidation. It is also found that a single DEFC of Pt/Sn atomic ratioless than or equal to2, "Pt1Sn1/C, Pt3Sn2/C, and Pt2Sn1/C" shows better performance than those with Pt3Sn1/C and Pt4Sn1/C. But even adopting the least active PtSn catalyst, Pt4Sn1/C, the DEFC also exhibits higher performance than that with the commercial Pt1Ru1/C, which is dominatingly used in PEMFC at present as anode catalyst for both methanol electro-oxidation and CO-tolerance. At 90 degreesC, the DEFC exhibits the best performance when Pt2Sn1/C is adopted as anode catalysts. This distinct difference in DEFC performance between the catalysts examined here is attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and Sn. It is thought that -OHads, Surface Pt active sites and the ohmic effect of PtSn/C catalyst determines the electro-oxidation activity of PtSn catalysts with different Pt/Sn ratios. (C) 2004 Elsevier B.V. All rights reserved.

Magnetic resonance and conductivity study of gelatin-based proton conductor polymer electrolytes

This work report results from proton nuclear magnetic resonance (NMR), continuous-wave (CW-EPR) and pulsed electron paramagnetic resonance (P-EPR) and complex impedance spectroscopy of gelatin-based polymer gel electrolytes containing acetic acid. cross-linked with formaldehyde and plasticized with glycerol. Ionic conductivity of 2 x 10(-5) S/cm was obtained at room temperature for samples prepared with 33 wt% of acetic acid. Proton ((1)H) line shapes and spin-lattice relaxation times were measured as a function of temperature. The NMR results show that the proton mobility is dependent on acetic acid content in the plasticized polymer gel electrolytes. The CW-EPR spectra, which were carried out in samples doped with copper perchlorate, indicate the presence of the paramagnetic Cu(2+) ions in axially distorted sites. The P-EPR technique, known as electron spin echo envelope modulation (ESEEM), was employed to show the involvement of both, hydrogen and nitrogen atoms, in the copper complexation of the gel electrolyte. (C) 2009 Elsevier Ltd. All rights reserved.

7Li NMR measurements of polymer gel electrolytes

Ion conducting polymer gels prepared from (ethylene oxide)_n grafted methacrylates, ethylene carbonate (EC), gamma butyrolactone (gBL), and lithium hexafluorophosphate are studied by means of nuclear magnetic resonance spectroscopy. This study shows that there are at least two possible lithium sites with different mobility. The lithium-ions with lower mobility dominate at room temperature, but this is changed as the temperature is increased. The NMR results also show that the ⁷Li spin–spin relaxation time decreases with increasing length of the grafted ethylene oxide side chains, indicating a stronger interaction between the polymer and the Li-ions, and hence, a lower mobility of the Li-ions.

Enhance the optical absorptivity of nanocrystalline TiO2 film with high molar extinction coefficient ruthenium sensitizers for high performance dye-sensitized solar cells

We report two new heteroleptic polypyridyl ruthenium complexes, coded C101 and C102, with high molar extinction coefficients by extending the pi-conjugation of spectator ligands, with a motivation to enhance the optical absorptivity of mesoporous titania film and charge collection yield in a dye-sensitized solar cell. On the basis of this C101 sensitizer, several DSC benchmarks measured under the air mass 1.5 global sunlight have been reached.

Dye-sensitized solar cells with solvent-free ionic liquid electrolytes

We systematically studied the temperature-dependent physicochemical properties, such as density, conductivity, and fluidity, of 1,3-dialkylimidazolium iodides. In combination with the amphiphilic Z907Na sensitizer, we have found that it is important to use low-viscosity iodide melts with small cations to achieve high-efficiency dye-sensitized solar cells. By employing high-fluidity eutectic-based melts the device efficiencies considerably increased compared to those for cells with the corresponding state of the art ionic liquid electrolytes.

Desenvolvimento de redes de polímeros interpenetrantes (IPN) para a aplicação como eletrólito polimérico

Uma nova rede de polímeros interpenetrantes (IPN) baseada em poliuretana de óleo de mamona e poli(etileno glicol) e poli(metacrilato de metila) foi preparada para ser utilizada como eletrólito polimérico. Os seguintes parâmetros de polimerização foram avaliados: massa molecular do poli(etileno glicol) (PEG), concentração de PEG e concentração de metacrilato de metila. As membranas de IPN foram caracterizadas por calorimetria diferencial de varredura (DSC) e espectroscopia de infravermelho por transformada de Fourier (FT-IR). Os eletrólitos de redes de polímeros interpenetrantes (IPNE) foram preparados a partir da dopagem com sal de lítio através do inchamento numa solução de 10% em massa de LiClO4 na mistura de carbonato de etileno e carbonato de propileno na razão mássica de 50:50. As IPNEs foram caracterizadas por espectroscopia de impedância eletroquímica e Raman. As IPNEs foram testadas como eletrólito polimérico em supercapacitores. As células capacitivas foram preparadas utilizando eletrodos de polipirrol (PPy). Os valores de capacitância e eficiência foram calculados por impedância eletroquímica, voltametria cíclica e ciclos galvonostáticos de carga e descarga. Os valores de capacitância obtidos foram em torno de 90 F.g-1 e eficiência variou no intervalo de 88 a 99%. Os valores de densidade de potência foram superiores a 250 W.kg-1 enquanto que a densidade de energia variou de 10 a 33 W.h.kg-1, dependendo da composição da IPNE. As características eletroquímicas do eletrólito formado pela IPN-LiClO4 (IPNE) foram comparadas aos eletrólitos poliméricos convencionais, tais como poli(difluoreto de vinilideno)-(hexafluorpropileno) ((PVDF-HFP/LiClO4) e poliuretana comercial (Bayer desmopan 385) (PU385/LiClO4). As condutividades na temperatura ambiente foram da ordem de 10-3 S.cm-1. A capacitância da célula utilizando eletrodos de PPy com eletrólito de PVDFHFP foi de 115 F.g-1 (30 mF.cm-2) e 110 F.g-1 (25 mF.cm-2) para a célula com PU385 comparadas a 90 F.g-1 (20 mF.cm-2) para a IPNE. Os capacitores preparados com eletrólito de IPNE apresentaram valores de capacitância inferior aos demais, entretanto provaram ser mais estáveis e mais resistentes aos ciclos de carga/descarga. A interpenetração de duas redes poliméricas, PU e PMMA produziu um eletrólito com boa estabilidade mecânica e elétrica. Um protótipo de supercapacitor de estado sólido foi produzindo utilizando eletrodos impressos de carbono ativado (PCE) e o eletrólito polimérico de IPNE. A técnica de impressão de carbono possui várias vantagens em relação aos outros métodos de manufatura de eletrodos de carbono, pois a área do eletrodo, espessura e composição são variáveis que podem ser controladas experimentalmente. As células apresentaram uma larga janela eletroquímica (4V) e valores da capacitância da ordem de 113 mF.cm-2 (16 F.g-1). Métodos alternativos de preparação do PCE investigados incluem o uso de IPNE como polímero de ligação ao carbono ativado, estes eletrodos apresentaram valores de capacitância similares aos produzidos com PVDF. A influência do número de camadas de carbono usadas na produção do PCE também foi alvo de estudo. Em relação ao eletrólito polimérico, o plastificante e o sal de lítio foram adicionados durante a síntese, formando a IPNGel. As células apresentaram alta capacitância e boa estabilidade após 4000 ciclos de carga e descarga. As membranas de IPN foram testadas também como reservatório de medicamento em sistemas de transporte transdérmico por iontoforese. Os filmes, mecanicamente estáveis, formaram géis quando inchado em soluções saturadas de lidocaina.HCl, anestésico local, em propileno glicol (PG), poli(etileno glicol) (PEG400) e suas misturas. O grau de inchamento em PG foi de 15% e 35% em PEG400. Agentes químicos de penetração foram utilizados para diminuir a resistência da barreira causada pela pele, dentre eles o próprio PG, a 2-pirrolidinona (E1) e a 1-dodecil-2-pirrolidinona (E2). Os géis foram caracterizados por espectroscopia de impedância eletroquímica e transporte passivo e por iontoforese através de uma membrana artificial (celofane). O sistema IPN/ lidocaina.HCl apresentou uma correlação linear entre medicamento liberado e a corrente aplicada. Os melhores resultados de transporte de medicamento foram obtidos utilizando o PG como solvente.

Novel organic-inorganic composite polymer-electrolyte membranes for DMFCs

Organic-inorganic composite membranes comprising Nation with inorganic materials such as silica, mesoporous zirconium phosphate (MZP) and mesoporous titanium phosphate (MTP) are fabricated and evaluated as proton-exchange-membrane electrolytes for direct methanol fuel cells (DMFCs). For Nation-silica composite membrane, silica is impregnated into Nation matrix as a sol by a novel water hydrolysis process precluding the external use of an acid. Instead, the acidic nature of Nation facilitates in situ polymerization reaction with Nation leading to a uniform composite membrane. The rapid hydrolysis and polymerization reaction while preparing zirconia and titania sols leads to uncontrolled thickness and volume reduction in the composite membranes, and hence is not conducive for casting membranes. Nafion-MZP and Nafion-MTP composite membranes are prepared by mixing pre-formed porous MZP and MTP with Nation matrix. MZP and MTP are synthesised by co-assembly of a tri-block co-polymer, namely pluronic-F127, as a structure-directing agent, and a mixture of zirconium butoxide/titanium isopropoxide and phosphorous trichloride as inorganic precursors. Methanol release kinetics is studied by volume-localized NMR spectroscopy (employing ``point resolved spectroscopy'', PRESS), the results clearly demonstrating that the incorporation of inorganic fillers in Nation retards the methanol release kinetics under osmotic drag. Appreciable proton conductivity with reduced methanol permeability across the composite membranes leads to improved performance of DMFCs in relation to commercially available Nafion-117 membrane.

Nafion and modified-Nafion membranes for polymer electrolyte fuel cells: An overview

Polymer electrolyte fuel cells (PEFCs) employ membrane electrolytes for proton transport during the cell reaction. The membrane forms a key component of the PEFC and its performance is controlled by several physical parameters, viz. water up-take, ion-exchange capacity, proton conductivity and humidity. The article presents an overview on Nafion membranes highlighting their merits and demerits with efforts on modified-Nafion membranes.

Enhanced Proton Conduction in Polymer Electrolyte Membranes as Synthesized by Polymerization of Protic Ionic Liquid-Based Microemulsions

Proton-conducting membranes were prepared by polymerization of microemulsions consisting of surfactant-stabilized protic ionic liquid (PIL) nanodomains dispersed in a polymerizable oil, a mixture of styrene and acrylonitrile. The obtained PIL-based polymer composite membranes are transparent and flexible even though the resulting vinyl polymers are immiscible with PIL cores. This type of composite membranes have quite a good thermal stability, chemical stability, tunability, and good mechanical properties. Under nonhumidifying conditions, PIL-based membranes show a conductivity up to the order of 1 x 10(-1) S/cm at 160 degrees C, due to the well-connected PIL nanochannels preserved in the membrane. This type of polymer conducting membranes have potential application in high-temperature polymer electrolyte membrane fuel cells.

Blends based on sulfonated poly[bis(benzimidazobenzisoquinolinones)] and poly(vinylidene fluoride) for polymer electrolyte membrane fuel cell

A new blend system consisting of an amorphous sulfonated poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI) and the semi-crystalline poly(vinylidene fluoride) (PVDF) was prepared for proton exchange membranes. The miscibility behavior of a series of blends of SPBIBI with PVDF at various weight ratios was studied by WXRD, DSC and FTIR. The properties of the blend membranes were investigated, and it was found that the introduction of PVDF in the SPBIBI matrix altered the morphological structure of the blend membranes, which led to the formation of improved connectivity channels. For instance, the conductivity of the blend membrane containing 10 wt% PVDF displayed the highest proton conductivity (i.e., 0.086 S cm(-1)) at room temperature, a value almost twofold that of the pristine SPBIBI membranes (i.e., 0.054S cm(-1)) under identical conditions.

Electrochemical H2S sensor with H2SO4 pre-treated Nafion membrane as solid polymer electrolyte

It is reported for the first time that the performance of the electrochemical H2S sensor with the Nation membrane pre-treated with the concentrated H2SO4 as the solid electrolyte is much more stable than that for the sensor with the Nation membrane without H2SO4 pretreatment. The sensitivity of the sensor is about 2.92 muA/ppm. The response time of the sensor is about 9 s. The detection limit is about 0.1 ppm. Therefore, this kind of the electrochemical H2S gas sensor may be desirable for the practical application.

A study on the diffusion of quinhydrone in polymer electrolyte

The diffusion coefficients (D) of quinhydrone were estimated in polymer electrolytes by using non-steady-state chronoamperometry and steady-state current voltammetry. The D values have been estimated in polyethylene glycol (PEG) containing different concentrations, and cations of supporting electrolytes, and in different solvents over a range of temperatures. The dependencies of electroactive probe diffusion coefficients on temperature, supporting electrolyte concentration and polymer chain length are discussed. The results show that D increases with increasing temperature and decreasing concentration of supporting electrolyte. The diffusion coefficient depends strongly on the length of polymer chain and decreases sharply with increasing polymer chain length. The contribution of electron self-exchange has been explored and it seems to be negligible here. (C) 1998 Elsevier Science S.A.